1. Field of the Invention
The present invention relates to a mechanical fastener system suitable for reliably joining high-temperature composite structural assemblies.
2. Background Art
Load-bearing high temperature (i.e., hot) structures fabricated from ceramic composite materials are a promising option for manufacturing specialized components to be used in the manufacture of new high-speed aircraft, atmospheric entry vehicles and propulsion systems in order to advantageously reduce weight and increase operational performance and reliability. An important consideration in the design of such hot structures is the ability to be able to reliably join and hold the component parts together under the extreme loads to which such structures will be subjected. Large-area hot structures will likely be fabricated by mechanically joining smaller component sub-assemblies. Conventional metallic fasteners and fastening techniques have both limited application and ability to withstand high temperature and, consequently, do not provide structurally tight joints over a wide temperature range. A metallic fastener, which is snug at room temperature, will loosen at elevated temperature due to its relatively high thermal expansion. Excessive preloading at room temperature to maintain a tight joint at elevated temperature may be detrimental to the structural integrity of the joint.
Mechanical fasteners fabricated from thermo-elastically compatible ceramic composite materials, however, circumvent the inherent limitations of high-temperature metallic fasteners and thus offer an improvement over the performance of mechanically fastened joints in hot composite structures. Conventionally shaped ceramic composite fasteners can be designed to exhibit near-perfect thermo-elastic compatibility with the adjoining ceramic composite elements. Nevertheless, the prohibitively high cost to produce most conventional composite fasteners is a disadvantage that impedes their widespread utilization.
Therefore, it would be desirable to have available a method for making a cost-effective thermal stress-free ceramic composite mechanical fastener system that is suitable for joining high-temperature ceramic composite structural assemblies.